Adhesion of coatings to ethylene-polar monomer copolymer

ABSTRACT

The adhesion of coatings to ethylene-polar monomer copolymer substrates is enhanced by the use, as an adhesion promoter, of vinyl acetate polymer.

0 United States Patent 1151 3,637,428 Aleckner, Jr. 1 5] Jan. 25, 1972541 ADHESION OF COATINGS T0 3,088,844 5/1963 Hungerford ..117/13s.s E xETHYLENE POLAR MONOMER 3,205,077 9/1965 Hammond ..l17/138.8 E XCOPOLYMER 3,232,789 2/1966 Pelzek et al. ...1 l7/138.8 E 3,340,0919/1967 Zweig ..l17/138.8 E [72] Inventor: John F. Aleckner, Jr.,Bloomfield, NJ. 3,427,184 2/1969 Mauro "117/138-3 E x 3,442,687 5/1969Hagan ..117/l38.8 E X [73] Assignee: Union Carbide Corporation, NewYork,

N.Y. Primary Examiner-William D. Martin 22 Filed: Dec. 0 9 AssistantExaminer-Ralph l-lusack Att0rneyPaul A. Rose, Aldo J. Cozzi and James J.O'Connell [21] Appl. No.: 782,719 r r [52] [1.8. CI ..117/138.8 E,117/72, 117/76 F,

117/138.8 UA,117/16lUC,117/161UB [57] ABSTRACT E2 33 The adhesion ofcoatings to ethylene-polar monomer /76 A 61 0 l 8 copolymer substratesis enhanced by the use, as an adhesion promoter, of vinyl acetatepolymer. [56] References Cited 7 Claims, No Drawings ADHESION 01FCOATINGS TO ETI-IYLENE-POLAR MONOMER COPOLYMER BACKGROUND OF THEINVENTION 1. Field of the Invention The invention relates to the coatingof ethylene-polar monomer copolymer substrates.

2. Description of the Prior Art Ethylene-polar monomer copolymers, suchas ethylenevinyl acetate copolymers, have been used for a number ofapplications which require the use of such copolymers in the form of amolded or shaped object. The use of such copolymers for variousapplications, however, has been curtailed due to the fact that thecopolymers are clear materials which, generally, have poor paintabilityproperties. For many applications, plastic substrates must be paintedfor decorative or other purposes. Those in the art, however, have notbeen able to provide, prior to the present invention, a procedurewhereby ethylene-polar monomer copolymers, in general, may be readilypainted with a well-bonded paint. Where any substantial adhesion of apaint to such substrates was obtained a costly or time-consumingpretreatment of the surface of the substrate was usually required, suchas by treating the substrate by one or another procedure for oxidizingsuch surfaces such as by a treatment with flame, corona discharge orchromic acid. In many cases, moreover, the attempts to provide coatingsfor many ethylene-polar monomer copolymer substrates only led to theproduction of coatings which would crack and peel from the surface ofthe substrate when the substrate was flexed under actual or simulateduse conditions.

SUMMARY OF THE INVENTION The adhesion of coatings to ethylene-polarmonomer copolymer substrates is enhanced by the use, as an adhesionpromoter, of vinyl acetate polymer.

An object of the present invention is to provide a means for improvingthe adhesion of coatings to ethylene-polar monomer copolymer substrates.

DESCRIPTION OF THE PREFERRED EMBODIMENTS It has been found that theadhesion of various paints or other coatings to ethylene-polar monomercopolymer substrates may be greatly enhanced by the utilization, as anadhesion promoter, of vinyl acetate polymer.

THE SUBSTRATE The substrates which are to be coated in accordance withthe teachings of the present invention are copolymers of ethylene andone or more polar monomers. These substrate copolymers are solidmaterials under nonnal conditions, that is at 25 C. They will containabout 20 to 95 weight percent of ethylene and about 5 to 80 weightpercent of polar monomer. They include all the copolymer materials whichare commonly employed for the fabrication of ethylene-polar monomercopolymer-based molded or shaped articles. Such copolymers include thosewhich have melt indices of about 0 to 100 and densities ofabout 0.925 to0.970.

The term polar monomer is used in the present specification and claimsto denote a substituted a-olefin which readily copolymerizes withethylene and contains a functional group, incorporates a hetero atom,and contributes to a measurable dipole moment. This differentiates fromother a-olefins such as propylene, butylene, hexene and the like whichdo not have hetero atoms nor readily measurable dipole moments.

Illustrative of the polar monomers and mixtures thereof which can becopolymerized with ethylene to form the substrate copolymers which canbe utilized in accordance with the present invention are the following:vinyl and vinylidene halides such as vinyl chloride, vinylidenechloride, vinylidene bromide and the like; vinyl esters such as vinylformate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl2,4-dimethylpentoate, vinyl pelargonate, vinyl stearate, vinyl pivalate,vinyl tert-butylacetate, vinyl chloroacetate, vinyl chloropropionate,vinyl benzoate, vinyl chlorobenzoate, vinyl diethylacetate, vinyl beta,gamma-dimethyl valerate, vinyl thioacetate, vinyl alcohol and the like;acrylic and alpha-alkyl acrylic acids, their salts, their alkyl esters,their amides and their r'iitriles such as acrylic acid, chloroacrylicacid, methacrylic acid, ethacrylic acid, methyl acrylate, ethylacrylate, butyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate,n-decyl acrylate, lauryl acrylate, hexadecyl acrylate, octadecylacrylate, methyl methacrylate, butyl methacrylate, methyl ethacrylate,ethyl ethacrylate, acrylamide, N-methyl acrylamide, N,N-dimethylacrylamide, methacrylamide, N-methyl methacrylamide, N,N-dimethylmethacrylamide, methyl vinylacetamide, acrylonitrile,chloroacrylonitrile, methacrylonitrile, ethacrylonitrile, and the like;alkyl esters of maleic and fumaric acid such as dimethyl maleate,diethyl maleate and the like; vinyl alkyl esters and ketones such asvinyl methyl ether vinyl ethyl ether, vinyl isobutyl ether, 2chloroethylvinyl ether, methyl vinyl ketone, ethyl vinyl ketone isobutyl vinylketone and the like; also vinyl pyridine, N-vinyl carbazole, N-vinylpyrrolidine, ethyl methylene malonate and the like.

Because of the relative ease with which such substrates may be employedin the present invention the preferred copolymers are those of the vinylesters, particularly vinyl acetate, and the acrylic and alpha-alkylacrylic acids and the salts and alkyl esters of such acids. The salts ofthese acids inelude those formed from cations which are one, two andthree valence metals such as sodium, lithium, potassium, calciummagnesium, aluminum, barium, zinc, zirconium, beryllium iron, nickel,cobalt, and the like, and nonmetallic cations such as ammonium (NHf).

In addition to ethylene and the polar monomers, the substrate copolymersmay also contain minor amounts, i.e., up to about 5 weight percent, ofone or more other monomers which are copolymerizable with ethylene andthe polar monomers. Such other monomers would include other vinylcompounds, such as other monoolefins, such as propylene, isopropylene,l-butene, isobutylene, hexene, cyclohexene, and the like; polyolefinssuch as butadiene, isoprene, dicyclopentadiene, norbornene, and thelike; and vinyl aryls such as styrene, o-methylstyrene, p-methylstyrene, m-methyl styrene, p-phenyl styrene, o-phenyl styrene, m-phenylstyrene, vinyl naphthalene and the like.

The term vinyl" means a compound which contains polymerizable ethylenicunsaturation, i.e.,

The substrates which are employed in the present invention need not bepretreated with any mechanical or other pretreating procedures prior tothe use of the adhesion promoters of the present invention.

The ethylene-polar monomer copolymer substrate may be used in all thevarious forms in which such substrates have commonly been employed bythose in the art, such as in the form of solid, porous or foamedstructures. The substrates may also be in any configuration such as filmsheet, strip, rod or other molded or shaped configuration.

The substrates may also be in a rigid or plasticized condition. The termrigid means that the substrate contains less than about 5 percent byweight, based on the weight of the ethylene-polar monomer copolymer inthe substrate, of one or more liquid plasticizers. The term plasticizedmeans that the substrate contains more than such amounts of liquidplasticizers.

In addition to plasticizers, the ethylene-polar monomer copolymersubstrates may contain other adjuvants which are commonly employed withethylene-polar monomer copolymers in the fabrication of molded objects.Such other adjuvants would include impact modifiers, fillers,lubricants, stabilizers, coloring agents, processing aids and the like.The amounts of the adjuvants that are employed are those which areeffective for the intended purpose. Thus, the effective amount ofplasticizer, for example, is a plasticizing amount, that is, an amountof plasticizer which will appreciably increase the flexibility,processability, workability and/or distensibility of the polymer.

Applications for which the ethylene-polar monomer copolymer substratesmight be used when coated in accordance with the present invention arethe following: functional or decorative items for automobiles such ashead restraints, door knobs, arm rests, bezels, trim, and the like;toys; traffic cones; sporting goods, such as decoys and buoys; andfurniture coverings.

THE ADHESION PROMOTER The adhesion promoter which is used in accordancewith the present invention is a vinyl acetate polymer. This polymer maybe a homopolymer of vinyl acetate or it may be a copolymer of vinylacetate and one or more other monomers, including ethylene, which may becopolymerizable therewith. Such other monomers would include all thoseenumerated above with respect to the monomers they may be copolymerizedwith ethylene to form the substrate copolymers. The preferred adhesionpromoter copolymers are those which contain about 2 to 77 weight percentof one or more monomers other than vinyl acetate, and the most preferredof such vinyl acetate copolymers are those which contain about 2 to 77weight percent of ethylene and about 23 to 98 weight percent of vinylacetate.

The polymers which are used as the adhesion promoters in the presentinvention are normally solid at room temperature. They have densities ofabout 0.94 to 1.0.

Both the copolymer which is used as the substrate and the polymer whichis used as the adhesion promoter may be made by techniques commonlyknown to those in the polymerization art.

The adhesion promoter polymer of the present invention may be usedeither as a prime coating or paint, or as an additive in a topcoating orpaint in accordance with the teachings of the present inventionv Theterm coating or paint" as used with respect to the present inventionmeans a coating or paint that may be thinned with a solvent that is asolvent for the vinyl acetate polymers that are used as the adhesionpromoters. Such solvents would include aromatic hydrocarbons, such asbenzene, xylene, toluene and coal tar naphtha; ketones; such as acetone,methyl ethyl ketone and methyl isobutyl ketone; esters, such asisopropyl acetate and n-butyl acetate; ethers, such as dioxane;chlorinated hydrocarbons, such as dichloroethylene and trichloroethyleneand others, such as mineral spirits (petroleum distillate, B.P. of about300-385 F By the term solvent" it is meant an organic liquid which willdissolve at least weight percent of the vinyl acetate polymer at 60 C.and will retain at least 10 weight percent of the polymer in solution atroom temperature.

USE OF THE ADHESION PROMOTER IN THE TOPCOAT The vinyl acetate polymeradhesion promoter of the present invention may be added directly to atopcoating which is to be applied directly to the ethylene-polar monomercopolymer substrate. When the vinyl acetate polymer adhesion promoter isused as an additive in a topcoat painting or coating, it should be usedin an amount which corresponds to about 10 to 70 percent by weight ofthe topcoat, based on the nonvolatile component contents of the topcoat.

THE TOPCOATS The topcoats which may be employed with the vinyl acetatepolymer adhesion promoter of the present invention include coatingswhich are useful for indoor and outdoor applications and for functionaland decorative purposes. Such coatings usually contain one or morevolatile and/or nonvolatile vehicles, and one or more pigments orextenders. One of more driers may also be used to accelerate the dryingof the nonvolatile vehicles. Plasticizers may also be used in thetopcoating as flexibilizers or extenders. The amounts of the componentsof the coatings or paints, other than the adhesion promoter of thepresent invention, are known to those in the art, and they are dictatedby the application.

The volatile vehicles include all those solvents in which the vinylacetate polymer adhesion promoter is soluble and in which thenonvolatile vehicles may be dissolve or dispersed. The volatile vehicleis usually employed to reduce the viscosity of the nonvolatile vehiclesto a more easily handled consistency so as to ease the brushability ofthe coating and provide the fluidity and stability which are needed forease of mixing. After the application of the topcoat to the substrate,the volatile vehicles are allowed to evaporate, leaving behind thenonvolatile vehicle to bind the pigment particles to each other and alsoprovide a continuous coating for the substrate.

The nonvolatile vehicles include all those commonly employed in thepaint or coating arts which may be dissolved or dispersed in a solventfor vinyl acetate polymer. Such nonvolatile vehicles include resins suchas natural and synthetic rubber; drying oils; rosin and rosinderivatives; synthetic resins such as alkyd resins; polyolefins,including polyethylene, chlorinated polyethylene, sulfonatedpolyethylene, polypropylene and ethylene-propylene copolymers; vinylresins such as polyvinyl fluoride, polyvinylidene fluoride, polyvinylchloride, polyvinylidene chloride, polyvinyl acetate, polyvinylacetal,polyvinyl butyral and polyvinyl alcohol; cellulosic resins such ascellulose nitrate and cellulose acetate resins; phenolic resins such asphenolformaldehyde resins; urea and melamine resins; polystyrene; epoxyresins; acrylic resins; silicone resins; polycarbonate resins;polysulfone resins; polyaryl ether resins and the like.

The driers that may be used include salts of various metals. The metalsmost frequently used to form the drier salts are cobalt, lead, zinc,manganese and calcium. The salts are usually naphthenates, oleates orresinates.

The pigments or extenders that may be used include lead oxide, zincoxide, anatase and rutile titanium dioxide, antimony oxide, basiccarbonate white lead, basic sulfate white lead, basic silicate whitelead, leaded zinc oxide, zinc sulfide, lithopone, lead tetraphosphate,zirconium oxide, calcium sulfate, silica, carbon black, red iron oxide,yellow iron oxide, red lead, cadmium sulfide, cadmium lithopones,cadmium sulfoselenides, cuprous oxide, raw and burnt umber, manganite,lead chromates, zinc chromate, zinc tetraoxychromate, chrome greens,chromic oxide, iron blues, cobalt blue, metallic powders of aluminum,copper, bronze, zinc, lead, gold, silver, tin, nickel and stainlesssteel; and various organic dyes and pigments.

USE OF ADHESIVE PROMOTER AS PRIMER The vinyl acetate polymer adhesionpromoter of the present invention may be used in solution as a primercoating to prime coat the surface of the substrate for the reception ofa top coat of another composition. When so used as a primer, the vinylacetate polymer is preferably dissolved in a solvent therefor so as toprovide a solution which will contain at least 10 percent by weight ofthe vinyl acetate polymer. The primer coating must also contain, inaddition to solvent and the vinyl acetate polymer, at least about 10weight percent, based on the nonvolatile component contents of theprimer coating, of the nonvolatile vehicle which is to be employed inthe topcoat.

The primer coating may also contain up to about 5 weight percent of oneor more nonvolatile plasticizers, based on the nonvolatile componentcontents of the primer coating. Such plasticizers would includephosphate esters, such as tricresyl phosphate, cresyl diphenylphosphate, and octyl diphenyl phosphate; phthalate esters, such asdioctyl phthalate, benzyl cyclohexyl phthalate, butylbenzyl phthalate,cresyl benzyl phthalate, (ll-2 -ethyl hexyl phthalate, butyl phthalylbutyl glycolate and dioctyl phthalate; and epoxy resins, such as butylepoxy stearate, epoxidized soy bean oil and epoxidized peanut oil.

The primer coating may also include other adjuvants to control orfacilitate the application and drying of the primer coating and thetopcoating.

The primer coating is usually applied to the substrate so as to providea layer of primer which is about 0.25 to 1 mil thick after the solventis removed therefrom.

When the vinyl acetate polymers are used as adhesion promoters in theform of a primer coating, the topcoating which is thereafter applied tothe thus primed substrate need not contain any of the vinyl acetatepolymer adhesion promoter. The topcoats which may be employed in thisregard include all those described above.

Both the primer coating and the topcoating may be applied by any of thecommonly employed techniques for applying primers and coatings tosubstrates such as dip coating, roller coating, knife coating, slushcoating and spraying.

In preparing the primer or topcoat compositions, it is preferable thatthe soluble components of such systems be admixed with the solventcomponents that are to be employed, at elevated temperatures, in orderto dissolved all of such soluble materials therein and then to add theinsoluble components to the resulting solutions. The admixture of allthe components may be accomplished in a homogenous fashion by any of thecommonly employed techniques which are used for this purpose such asball milling, paint milling, pebble milling and roll mixing. The reducedviscosity values were computed by use of the equation:

Reduced viscosity t,t,, /(ct wherein t is the efflux time of the solventfor the polymer, t, is the efflux time of the solution of the polymerand c is the concentration of the polymer solution in terms of grams ofpolymer per 100 ml. of solvent.

The following examples are merely illustrative of the present inventionand are not intended as a limitation upon the scope thereof.

EXAMPLES A In these examples various topcoat formulations were employedwith an adhesion promoter additive of the present invention. Theseformulations, that is I-Ill, are clear formulations, but they could bepigmented or extended with one or more of the pigments or extenderslisted above. In preparing the topcoat formulations the vinyl acetatepolymer which was employed as the adhesion promoter was dissolved in aportion of the solvent system at an elevated temperature of about 60 C.This solution was then added to a solution of the resin in the remainingsolvent and placed in a container and mixed on a can roller for about tominutes. The formulations that were employed were the following:

I. vinyl resin based formulations III. acrylic-nitrocellulose resinbased formulation weight percent acrylic resin lit-second nitrocelluloseresin solution ethylene-vinyl acetate copolymer 5.35 n-butyl acetate26.00 isopropyl acetate 9.55 toluene 26.00 xylene 12.75

vinylchloride-vinylacetate-vinyl alcohol terpolymer which contains suchmonomers in a 91/36% weight ratio and which has a viscosity of 315centipoises as a 20% solids content solution in MIBK.

ethylene-vinylacetate copolymer adhesion promoter which contains suchmonomers in a 72/28% weight ratio and which has a density of 0.95 and amelt index of 350.

ethylenevinylacetate copolymer adhesion promoter which contains suchmonomers in a 67/33% weight ratio and which has a density of 0.955 and amelt index of 20.

methylmethacrylate-ethyl acrylate copolymer which contains such monomersin a 75/25% weight ratio and which has a viscosity of LOGO-2,500centistokes as a 40% solids content solution in toluene.

solution contained, be weight,

a) 20% lit-second RS nitrocellulose b) 24% toluene c) 56% methyl ethylketone These formulations were applied to the following substrates whichwere in the form of solid sheets about 30 to mils thick:

a. ethylene-vinylacetate copolymer which contained 82 percent by weightof ethylene and 18 percent by weight of vinylacetate and had a densityof 0.94 and a melt index of 2.5,

b. ethylene-ethyl acrylate copolymer which contained 82 percent by weighof ethylene and 18 percent of ethyl acrylate and had a density of 0.931and a melt index of 6, and

c. ethylene-acrylic acid copolymer which contained 86 percent by weightof ethylene and 14 percent by weight of acrylic acid and had amelt indexof 5.

The topcoatings were applied by dip coating or by spraying so as toprovide the substrate, after the removal of the solvents in thetopcoating, with a layer of topcoat which was of the order of about 0.5to 1.5 mils thick.

The adhesion of the coatings to the substrates was evaluated by aflexing and a crosshatch test.

In the flexing test the coated substrate was flexed once about underambient conditions. The flexing did not produce any cracking peeling ofthe paint from the substrate in all cases where the pain contained thevinyl acetate polymer adhesion promoter of the present invention. Wherethe adhesion promoter was not used in the paint, however, the paintsreadily cracked under the flexing test in all cases under the same testconditions.

In the crosshatch test a crosshatched pattern is cut in the surface ofthe painted sample with a razor blade. A piece of cellophane tape isthen placed over the crosshatched pattern and the tape is then removedin an attempt to lift the coating from the surface. In all thoseinstances where the crosshatch test was applied to a paint employing thevinyl acetate polymer adhesion promoter of the present invention, nopeeling of the paint occurred. However, where the same base paints wereemployed without the adhesion promoter of the present invention and thecoated substrates were subjected to the crosshatch test, the unmodifiedpaints were readily peeled from the substrates. In all cases thesubstrates were not treated in any fashion prior to the application ofany of the paint formulations thereto.

After the application of the modified or unmodified paints to thesubstrates, the paints were allowed to dry in air at ambienttemperatures of about 25 C. overnight before the commencement of any ofthe tests indicated above.

EXAMPLES B This series of example illustrates the use of a vinyl acetatepolymer adhesion promoter as an additive in a pigmented topcoating inaccordance with the present invention. The topcoat formulation used wasthe following:

This topcoat formulation was directly applied to untreated samplesofsubstrates (a) and (b) of examples A by dip coating so as to providedried coatings having a thickness of about one-half mil. The coatingsdry at room temperature overnight. The dried coatings were subjected tothe flexing and crosshatch tests described in examples A. The coatingsdid not crack or peel under such tests, whereas when the same coating isused, but without the inclusion of the vinyl acetate copolymer adhesionpromoter, the coatings fail these tests.

EXAMPLES C This series of examples illustrates the use of a vinylacetate polymer adhesion promoter in a primer coating, over which atopcoating is applied, in accordance with the present invention.

The primer coating had the following composition:

This primer coating was directly applied by spraying so as to provide,after drying, a coating of about %-to z-mil thickness on untreatedsamples of substrates (a) and (b) of examples A. The primer coatingsdried at room temperature in about 3 to 5 minutes.

After the primer coatings had dried a topcoating was directly applied byspraying so as to provide a dried topcoating about 1 mil thick. Thetopcoating employed had the following composition:

component i by weight a) 91/3/6 weight 56 vinyl chloride-vinyl acetatevinyl alcohol terpolymer of examples A 13.5 b) dioctyl phthalate 5.0 c)MIBK 42.5 d) toluene 33.5 e) xylene 5 .5

The topcoatings were dried at room temperature overnight. The driedtopcoatings were subjected to the flexing and crosshatch tests describedin examples A. The topcoatings did not crack or peel under such tests,whereas when the same topcoating is used, without a primer coatingcontaining the vinyl acetate polymer adhesion promoter of the presentinvention, the top coating fails to adhere.

What is claimed is:

1. An ethylene-polar monomer copolymer substrate having a coatingadhered thereto, which comprises a. an ethylene-polar monomer copolymersubstrate wherein said copolymer comprises 20 to 95 weight percent ofethylene and 5 to weight percent of polar monomer an wherein said polarmonomer is a vinyl ester, acrylic acid or alpha-alkyl acrylic acid, or asalt or alkyl ester of such acids, and b. a coating adhered to andsuperimposed on said substrate, said coating including, as a coatingadhesion promoter only, and in an amount corresponding to about 10 to 70weight percent of said coating, a vinyl acetate polymer, said vinylacetate polymer being a homopolymer of vinyl acetate or a copolymerwhich consists of about 2 to 77 weight percent ofethylene and about 23to 98 weight percent of vinyl acetate, and said coating being one thatmay be thinned with an organic solvent for said adhesion promoter. 2. Acoated substrate as in claim 1 in which the coating is paint.

3. A coated substrate as in claim 1 in which the adhesion promoter is avinyl acetate homopolymer.

4. A coated substrate as in claim 1 in which said adhesion promoter is acopolymer of vinyl acetate and ethylene.

5. A coated substrate as in claim 4 in which said polar monomer is vinylacetate.

6. A coated substrate as in claim 4 in which said polar monomer is ethylacrylate.

7. A coated substrate as in claim 4 in which said polar monomer isacrylic acid.

* i t i 1!

2. A coated substrate as in claim 1 in which the coating is paint.
 3. Acoated substrate as in claim 1 in which the adhesion promoter is a vinylacetate homopolymer.
 4. A coated substrate as in claim 1 in which saidadhesion promoter is a copolymer of vinyl acetate and ethylene.
 5. Acoated substrate as in claim 4 in which said polar monomer is vinylacetate.
 6. A coated substrate as in claim 4 in which said polar monomeris ethyl acrylate.
 7. A coated substrate as in claim 4 in which saidpolar monomer is acrylic acid.